NEW YORK, Sept 30 (Reuters) - A U.S. judge said Germany"s Allianz SE (ALVG.DE) must face investor claims it wrongly "abandoned" the investment strategies it promised to use on hedge funds that suffered massive losses as the COVID-19 pandemic shook markets early last year. In an 81-page decision, U.S. District Judge Katherine Polk Failla in Manhattan said investors could try to show Allianz was negligent and lacked good faith in managing its Structured Alpha funds. She also dismissed some state law-based claims. Thursday"s decision addressed 12 lawsuits, including two proposed class actions, in which investors claimed to suffer more than $4 billion of losses. The insurer faces more than two dozen such lawsuits, seeking at least $6 billion. Allianz"s funds used complex option strategies to generate predictable returns without excessive risk, but according to the investors, imploded in February and March 2020 after quietly removing hedges designed to minimize losses. According to court papers, the Structured Alpha Global Equity 500 fund lost three-quarters of its value, lagging its benchmark by nearly 60 percentage points. Two other funds once worth $2.3 billion were liquidated, locking in investor losses. Failla said the investors could try to show that Allianz breached terms of a private placement memorandum for the funds, which she said the insurer portrayed as a "glorified advertising brochure, the substance of which [it] could ignore at will." Allianz and its lawyers did not immediately respond to requests for comment. Lawyers for investors in the proposed class actions did not immediately respond to similar requests. On Thursday, Allianz said its top asset management executive Jacqueline Hunt was leaving her day-to-day role, and announced changes to its board. read more The changes follow Allianz"s Aug. 1 announcement that the U.S. Department of Justice was investigating the Structured Alpha funds. That probe includes a review of whether Allianz fund managers misrepresented the funds" risks to investors, three people with knowledge of the matter said earlier in September. read more Another U.S. regulator, the U.S. Securities and Exchange Commission, is also probing the funds" collapse. The cases include In re Allianz Global Investors US LLC Alpha Series Litigation, U.S. District Court, Southern District of New York, No. 20-05615. Reporting by Jonathan Stempel in New York; Editing by Cynthia Osterman